Thunder Mesh works exclusively with the Microsoft Phone System in Office 365.  Phone System in Office 365 is Microsoft's technology for enabling call control and PBX capabilities in the Office 365 cloud with Skype for Business Online. Phone System allows you to replace your existing PBX system with a set of features delivered from Office 365 and tightly integrated into the company's cloud productivity experience.

With Phone System in Office 365, your users can use Skype for Business Online to take care of basic call control tasks, such as placing and receiving calls, transferring calls, and muting and unmuting calls. Phone System users can click a name in their address book, and Skype for Business places a call to that person. To place and receive calls, Phone System users can use their mobile devices, a headset with a laptop or PC, or one of many IP phones that work with Skype for Business. For administrators, Phone System provides the ability to manage calling within the same Tenant admin console used for messaging, collaboration, and so on.
As with traditional PBX systems and with Enterprise Voice, calls between users in your organization are handled internally within Phone System, never going to the PSTN. This applies to calls between users in your organization located in different geographical areas, removing long-distance costs on these internal calls. ​